An objective of semiconductor device manufacturing is to scale device dimensions in order to reduce channel resistance, and hence improve transconductance over previous technology nodes employing longer channel length. Unfortunately, due to the high electric field velocity saturation and/or increased Coulomb scattering due to higher body doping requirements, scaling of the devices has become ever more difficult in nanoscale Si channel devices.
In order to continue the scaling of the devices and in order to continue the increase in performance, strained silicon channels have been employed in semiconductor device manufacturing. The strain levels in the channel have been continuously increased to lower the channel resistance to meet the performance targets. However, this approach is also approaching saturation in mobility enhancement in Si technologies.